STANFORD — Some day — when your heart needs healing, your bones need bonding or your skin needs stitching — clusters of new cells now growing in a Stanford University lab could offer a fix.

For the first time, researchers at Stanford’s School of Medicine have quickly and efficiently generated pure colonies of 12 different specialized cell types from embryonic stem cells that could be used to repair the human body.

These various cells have been grown before, but the process has been fiendishly difficult to control. Experiments often ended up with impure mixtures of multiple cell types, with limited practical use. And it took a long time — weeks or months — to grow them.

The Stanford team, collaborating with the Genome Institute of Singapore, grew the cell colonies in mere days. This was made possible by the team’s improved understanding of the complex symphony of chemical signals needed to direct cellular development.

“It is fantastic — a gateway to a lot of applications in regenerative medicine,” a field that uses cells to build healthy replacement tissue, said Kyle Loh of Stanford’s Institute for Stem Cell Biology and Regenerative Medicine, a co-author of the study published in Thursday’s issue of the journal Cell. The work was supported, in part, by the California Institute for Regenerative Medicine, created by California voters when they approved $3 billion in bonds in 2004.

It represents another step toward the once seeming sci-fi fantasy of repairing or restoring damaged tissue with stem cells. Last week, physicians at Santa Clara Valley Medical Center, in partnership with Stanford Medicine, successfully completed a surgery injecting millions of stem cells into the spinal cord of a patient who had recently suffered a severe spinal cord injury. The aim is to replace damaged neural connections, restoring mobility. The unidentified patient, who is healing successfully, became one of only a handful of people in the world who have undergone the procedure as part of this clinical trial.

Ever since they were first isolated in 1998, embryonic stem cells have become one of medicine’s greatest hopes — and one of its biggest frustrations.

Extracted from early embryos, they are the body’s building blocks, capable of generating over 1,000 cells. This means they could be enlisted to build replacement organs or “diseases in a dish,” where drugs can be easily tested.

But it’s been challenging to replicate the exact developmental signals that embryos used to guide their development.

“It’s like assembling a new car,” Loh said. “You need to know how it’s put together, in what order and what arrangement.”

The Stanford-Singapore team created a detailed map of the routes through which stem cells develop into multiple cell types. They focused on the stem cells for the mesoderm, one of the three primary masses of cells in the early embryo. It is responsible for crafting bone, heart, blood vessels, cartilage, portions of the kidneys and skin and other cell types.

Then, using chemicals and proteins, they carefully guided the cells’ choices at each fork along the developmental road.

“We were able to get the precise timing and precise combination” of developmental signals, Loh said. San Jose native Angela Chen of San Jose State University and Stanford also shared in the research.

This forced the cells to follow specific paths — generating pure populations of desired cell types. The identify of the cells was verified through genetic analysis.

At the Stanford lab, Loh watched the uniformly round stem cells morph into different shapes, then “crawl away from one another, and move around the dish.”

Within five to nine days, it was possible to generate pure cell populations of almost all of the desired cells, said Dr. Irving Weissman, director of Stanford’s stem cell institute and a co-author of the paper.

“These kinds of research advancements are tremendously encouraging; the potential to proliferate these crucial cell populations this quickly has significant clinical applications to address acute unmet medical needs,” said Morrie Ruffin, managing director of the Alliance for Regenerative Medicine, a Washington, D.C.-based nonprofit that advocates for research, investment and commercialization of research to repair and replace tissue that has been damaged by disease, injury or natural aging.

Hank Greely, director of Stanford’s Center for Law and the Biosciences, called the research “really, really important if it holds up.”

“The problems of making or isolating pure samples of one specific cell type has been a substantial barrier to medical uses of embryonic stem cells. This research looks like a way around that problem,” he said.

“There are still other problems that need to be resolved,” such as immune system rejection of the cells, Greely added. To prevent that, researchers are exploring how to use cells made not from embryos but from the patient’s own body. “But every major problem solved means we are one step closer to a possible solution — with great medical benefits.”

The team’s next step, probably within the next few years, is to show whether these cells develop into more complex tissues. Then perhaps they will be moved into animal testing.

Lisa M. Krieger is a science writer at The Mercury News, covering research, scientific policy and environmental news from Stanford University, the University of California, NASA-Ames, U.S. Geological Survey and other Bay Area-based research facilities. Lisa also contributes to the Videography team. She graduated from Duke University with a degree in biology. Outside of work, she enjoys photography, backpacking, swimming and bird-watching.